The average life expectancy for the patient with cystic fibrosis is 21 years. The disease is hereditary and homozygous recessive. Symptoms develop from birth. One common feature in the etiology of the disease is the presence of a factor in the plasma, sweat, and saliva which interferes with salt balance in normal tissues. This plasma factor has not been isolated and characterized. Nothing is known concerning the origin of the disease or the plasma factor. Present methods of screening for the early detection of the disorder and for heterozygous conditions are not quantitative (accurate). The purpose of this study is four-fold: (a) the isolation in pure form of some of this plasma factor, (b) the preparation of an antibody to the plasma factor and development of an immune assay for the plasma factor, (c) preparation of a large quantitiy of the plasma factor using the quantitative immune assay, and (d) preliminary chemical characterization of the factor. If the correlation between presence of the factor in the plasma and the disease state is absolute, then the antibody will be used as the basis for a quantitative immune assay for rapid and accurate detection of the disease state.